My research group is investigating the molecules and mechanisms that maintain chromosomes in order to control cell viability and proliferation. In particular, we study the enzyme telomerase, which consists of RNA and protein components and is centrally important to human cancer and aging, and how it prevents the erosion of telomeric DNA at chromosome ends during cell division.
As briefly outlined below, we are discovering and investigating (1) essential telomerase RNA functional elements and their mechanisms of action, (2) the molecular mechanisms that maintain telomere length, and (3) the molecular and cellular hallmarks of senescence caused by critically short telomeres.
The telomerase ribonucleoprotein (RNP) enzyme, telomeres, and senescence.
What is the physical organization of telomerase RNA and how does it relate to function?
I determined the secondary structure of the 1157-nt S. cerevisiae telomerase RNA while I was a postdoc and revealed that it functions as a flexible scaffold for the essential Est1 protein subunit. With NIH K99/R00 funding, my independent lab at Johns Hopkins University then demonstrated that this novel function for an RNA in a ribonucleoprotein complex also pertains to the other two S. cerevisiae telomerase holoenzyme-specific subunits, Ku and Sm7, as well as for the essential three-way junction in the evolutionarily distant fission-yeast telomerase RNA.
My lab has also discovered several essential well-conserved RNA structural features within yeast and human telomerase RNAs. The characteristics of some of the new elements demonstrate that telomerase RNAs also have functions beyond acting as a flexible scaffold for protein subunits.
We are now determining the binding interface between the RNA and the catalytic protein subunit (TERT) at the core of the RNP enzyme, the extent of flexibility of telomerase RNA in the holoenzyme, as well as new telomerase subunits and their functions.
How is the telomerase RNP enzyme regulated to maintain telomere length?
Telomerase is preferentially recruited to short telomeres to promote their extension, but how this occurs is not known. We recently discovered how telomerase is recruited to telomeres by its Ku subunit. This finding led us to a model for the molecular mechanism of telomere-length homeostasis in yeast, as well as why there are two telomerase-recruitment pathways, coordinated by the Ku and Est1 subunits. With an NIH R01 grant supporting this project, we are now testing our model for the molecular mechanism coordinating telomere-length homeostasis. One aim is to determine the arrangement of telomere proteins along chromosome ends to help learn how they “sense” telomere length to preferentially recruit telomerase to short telomeres.
What are the molecular and cellular hallmarks of senescence caused by telomere loss?
Using RNA-seq, we have determined the genome-wide transcriptional response of cells undergoing senescence due to erosion of telomeres, as well as the “survivors” that emerge subsequently. Several major findings have come from these RNA-seq data: (1) senescence has distinct phases, each with a signature of hundreds of differentially expressed genes; (2) senescence is characterized by upregulation of >100 novel lncRNAs; and (3) there are many induced cellular pathways. We are now actively identifying the roles of differentially expressed proteins and RNAs to define and characterize the hallmarks of cellular senescence caused by telomere erosion.